42 J. E. Hobbie 



Diptera larvae (MacLean 1974). Their total biomass lies between 1.3 and 

 5.1 g dry wt nl"^ which approximates the microbial biomass. 

 Enchytraeidae dominate and make up 50 to 75% of the invertebrate 

 biomass in all habitats. Most of these animals are aerobic; thus they are 

 found mainly in the top 2.5 cm. 



The relatively high densities and high biomass of invertebrates are, in 

 part, a result of long life cycles. For example, two species of craneflies 

 (Diptera) require at least 4 years to complete larval development. The 

 annelid worms also have long life cycles. Despite the large biomass, the 

 long lives of the soil invertebrates give rise to low productivity rates. 



The biomass of soil macroinvertebrates (Nematoda, Enchytraeidae, 

 Acarina, and Collembola) is positively correlated with net primary 

 production rates but negatively correlated with accumulated organic 

 matter. This implies that the greatest macroinvertebrate biomass occurs in 

 habitats with the highest rates of energy and nutrient turnover. There is 

 still an abundance of accumulated organic matter in all habitats, so the 

 correlation of biomass with energy and nutrient turnover may reflect the 

 better quality or greater abundance of microbes. Alternatively, the feeding 

 of the invertebrates on the microbes may stimulate microbial activity and 

 thus cause a greater removal of organic matter. 



ENERGY AND NUTRIENT CYCLING 



The information that supports the conclusions in the following 

 sections is given in Bunnell et al. (1975) and Brown et al. (in press). 



Energy 



The entire aboveground biomass of the dominant tundra plants, the 

 grasses and sedges, grows and dies each year. The belowground biomass 

 lives longer but still turns over in 2 to 12 years depending upon the species. 

 In addition, rootlets and root hairs last but a single season. Thus, there is a 

 large annual input of fixed chemical energy to the system. 



In view of the virtual absence of lemmings during the "lows" of the 

 population cycle, it is amazing to discover that, on the average, the 

 percentage of the primary production consumed by animals is higher at 

 Barrow than in most other ecosystems. Vertebrate carnivores are, on the 

 average, also very active relative to other ecosystems. In spite of this 

 activity of the vertebrates, more of the energy of the system passes through 

 the populations of soil saprovores, and especially microbivores, than 

 throughthe lemmings. 



